package 动态数组;

public class ArrayList<E> {
	/**
	 * 元素的数量
	 */
	private int size;
	
	private E[] elements;
	
	private static final int DEFAULT_CAPACITY = 10;
	private static final int ELEMENT_NOT_FOUND = -1;
	
	public ArrayList(int capaticy)
	{
		capaticy = (capaticy < DEFAULT_CAPACITY) ? DEFAULT_CAPACITY: capaticy;
		elements = (E[])new Object[capaticy];
	}
	public ArrayList()
	{
		this(DEFAULT_CAPACITY);
	}
	/**
	 * 清除所有元素
	 */
	public void clear() {
		for (int i = 0;i < size ; i++) {
			elements[i] = null;
		}
		size = 0;
	}
	
	
	
	/**
	 * 元素的数量
	 * @return
	 */
	public int size() {
		return size;
	}

	/**
	 * 是否为空
	 * @return
	 */
	public boolean isEmpty() {
		 return true;
	}

	/**
	 * 是否包含某个元素
	 * @param element
	 * @return
	 */
	public boolean contains(E element) {
		return indexOf(element) != ELEMENT_NOT_FOUND;
	}

	/**
	 * 添加元素到尾部
	 * @param element
	 */
	public void add(E element) {
		
	}

	/**
	 * 获取index位置的元素
	 * @param index
	 * @return
	 */
	public E get(int index) {
		rangeCheck(index);
		return elements[index];
	}

	/**
	 * 设置index位置的元素
	 * @param index
	 * @param element
	 * @return 原来的元素ֵ
	 */
	public E set(int index, E element) {
		rangeCheck(index);
		E old = elements[index];
		elements[index] = element;
		return old;
	}

	/**
	 * 在index位置插入一个元素
	 * @param index
	 * @param element
	 */
	public void add(int index, E element) {
		for(int i = size - 1;i >= index; i--) {
			elements[i + 1] = elements[i];
		}
		elements[index] = element;
		size++;
	}

	/**
	 * 删除index位置的元素
	 * @param index
	 * @return
	 */
	public int remove(int index) {
		rangeCheck(index);
		for (int i = index + 1; i < size-1; i++) {
			elements[i - 1] = elements[i];
		}
		size--;
		return 0;
	}

	/**
	 * 查看元素的索引
	 * @param element
	 * @return
	 */
	public int indexOf(E element) {
		for (int i = 0;i < size;i++)
		{
			if (elements[i] == element) return i;
		}
		return ELEMENT_NOT_FOUND;
	}
	
	/**
	 * 保证要有capacity的容量
	 * @param capacity
	 */
	private void ensureCapacity(int capacity) {
		int oldCapacity = elements.length;
		if(oldCapacity >= capacity) return;
		
		int newCapacity = (oldCapacity >> 1) + oldCapacity;
		Object[] newElement = (E[])new Object[newCapacity];
		for(int i = 0; i < size;i ++) {
			newElement[i] = elements[i];
		}
		elements = newElement;
		
	}
	private void outOfBounds(int index)
	{
		throw new IndexOutOfBoundsException("Index:" + index + ",size:" + size);
	}
	private void rangeCheck(int index) {
		if (index < 0 || index >= size) {
			outOfBounds(index);
		}
	}
	
	@Override
	public String toString()
	{
		StringBuilder string = new StringBuilder();
		string.append("size=").append(size).append(",[");
		for(int i = 0;i <= size;i++)
		{
			string.append(elements[i]);
		}
		string.append("]");
		return string.toString();
	}
}
